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Friday, February 26, 2016

Efficacy of weed control: Ensuring successful cultivation of crops

By Bob Aston

Adopting an Integrated
weed management helps to ensure successful cultivation of crops. Speaking
during a Training of Trainers (TOT) workshop convened by the Agricultural
Sector Development Support Programme (ASDSP) on February 22-23, 2016 at the Agricultural
Machinery Services (AMS) Hall in Nyahururu, Mr. Lincoln Njiru, Laikipia County
Crops officer said that lack of a weed control plan leads to low production.

Mr. Lincoln Njiru emphasizing a point during the training

He said that weed control
during the first four to eight weeks after planting is crucial, because weeds
compete vigorously with the crop for nutrients and water during this period.

“The first critical
requirement for effective weed control is correct weed identification. Weeds
have special characteristics that tend to put them in the category of unwanted
plants,” said Mr. Njiru.

He said that weeds have
special characteristics that tend to put them in the category of unwanted
plants as they can withstand adverse conditions in the field and can germinate
under adverse soil moisture condition.

In addition, weed seeds
remain viable for longer period without losing their viability and they have a
short period of plant growth.

“Weeds that emerge at the
time of crop germination or within a few days of crop emergence cause greater
yield loss than weeds emerging later in the growing season,” said Mr. Njiru.

He urged farmers to adopt
integrated weed management, as it reduces weed interference with the crop while
maintaining acceptable crop yields.

Integrated weed
management approach ensures selection of adapted variety or hybrid seeds with
good early season vigor and appropriate disease and pest resistance. He urged
farmers to ensure weed free farm through cultural, mechanical, biological, or
chemical management.

Mechanical weed controls
involves pre-plant tillage, in row cultivation, and flaming weed control by use
of propane burners to kill the weeds by denaturing the proteins in the cell
membranes hence desiccating them.

Biological control
entails reuniting weeds with their natural enemies, although it is important
that they do not become pests themselves. Example is use of turkeys in fruit
orchards, commercial bio-herbicides, and tick berry against couch grass.

Chemical weed control
involves use of pre-emergence and post-emergence herbicides. Use of more than
one herbicide usually ensures a season long weed control.

“ High weed infestation
increases the cost of cultivation, lowers value of land, reduces the returns of
maize producers, reduce yield, make harvesting difficult, and lowers the
quality of grains,” said Mr. Njiru.

One of the participants contributing to a discussion

He said that some harmful
effects of weeds include loss of agricultural produce; reduced crop yields as
weeds compete with crops for water, soil, nutrients, light and space; some like
witch weeds are parasitic to maize; and some act as alternative hosts that
harbor insects, pests, diseases and other micro-organisms.

Other harmful effects of
weeds include reduction of quality of marketable agricultural produce, and release
into the soil inhibitors of poisonous substances that may be harmful to the
crop plants, human beings, and livestock by some weeds.

He noted that despite the
many harmful effect of weeds, some are beneficial as they help conserve soil
moisture and prevent erosion, and can be valuable indicators of growing
conditions in a field like water levels, compaction, and PH.

In addition, presence of
weed cover may be a factor in increasing effectiveness of biological control of
pests and reducing pest damage.

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